The present invention relates to an NC (Numerical Control) device by which a plurality of machining operations can be automatically performed on a plurality of groups of workpieces.
A conventional numerical control device of the same general type to which the invention relates is shown in FIG. 1. In FIG. 1, reference numeral 1 designates an NC control device; 2, a counter for counting the number of machining operations in response to the output of the NC device 1; 3, a switch device for presetting a required number of machining operations; 4, a machining program tape; 5, a display unit for indicating when a machining operation is accomplished; and 6, an NC machine tool.
In the conventional device, an instruction (MO 2, for instance) identifying the finish of machining is programmed at the end of the machining program tape 4. That instruction is reached after one cycle of machining has been accomplished. A count instruction is then outputted, whereupon the counter 2, which counts the number of machining operations, is incremented. When the count value of the counter 2 reaches the required number of machining operations instructed by the switch device 3, automatic machining is stopped and the display unit 5 is caused to indicate the fact that machining has been ended.
The conventional apparatus has only one counter for counting the number of machining operations for one group of workpieces to be machined at any one time. It cannot simultaneously perform machining operations on a plurality of groups of workpieces since it cannot count the number of actual machining operations in such a case. Furthermore, the conventional apparatus has no provision for specifying the order of machining. Therefore, when a predetermined number of machining operations has been performed on one group of workpieces, the apparatus cannot automatically select a next group of workpieces to continue the machining. That is, whenever a predetermined number of machining operations has been performed on one group of workpieces, a machining program must be separately inputted for the next group of workpieces and the required number of machining operations also must be preset. Therefore, with the conventional apparatus, it is difficult to establish a fully automatic system for a factory which handles small lots.
An object of the invention is thus to provide a numerical control device in which the above-described difficulties accompanying a conventional numerical control device have been eliminated, a desired number of machining operations can be preset for each of a plurality of groups of workpieces, the number of actual machining operations performed on workpieces counted for each group of workpieces, a machining order is set for the groups of workpieces, and machining operations of the groups of workpieces are controlled according to such data, whereby totally automatic machining operations can be carried out.